Hi, change the complete clutch with this type of engine is quite a waste. the original one with harder springs is good. you won't feel the difference with a complete clutch
if you want to improve the performance i suggest to spend your money to buy a good speed variator like Pinasco Overdrive or Polini 9 rollers or J Costa... i suggest the pinasco because it's supplied with a good quality spring and the spring-slyder special bearing... ;-)